I asked about HW because some of the new SPI controller IP have the delays programmable in HW. One from CS active to clock/data and the other is inter data delays.
Using HW SS and the timers it is built in. The issue is on a shared bus. We would need to extend the SPI API to support the settings. David -----Original Message----- From: Grr [mailto:gebbe...@gmail.com] Sent: Wednesday, March 24, 2021 10:52 AM To: dev@nuttx.apache.org Subject: Re: Sleep Resolution This is a SocketCAN driver for MCP2515 with a new SPI system that streamlines the select->write->read->deselect process and so exposes the need to guarantee hold time between read and deselect and disable time between deselect and next select Looking at David's code, it seems the loop is the right answer. The DWT cannot be used for a portable solution but maybe an inline function. Thanks for the idea I believe NOPs are optimized away but it seems asm("") or something close to that is not It would be nice to incorporate a general solution for this problem to the Nuttx toolbox El mié, 24 mar 2021 a las 11:24, David Sidrane (<david.sidr...@nscdg.com>) escribió: > What HW is this on? > > -----Original Message----- > From: Grr [mailto:gebbe...@gmail.com] > Sent: Wednesday, March 24, 2021 10:09 AM > To: dev@nuttx.apache.org > Subject: Re: Sleep Resolution > > Thank you very much for your response > > What I'm trying to do is to generate hold and disable times for SPI CS, > which should be about 50 ns > > I started by an empty for loop but it seems optimization gets rid of it (I > haven't researched the issue properly). Then I thought a proper function > would be better but got stuck in that expression "sleep resolution" > > For that scale (10 SYSCLK cycles), a loop is probably OK but I wanted to > make sure there's not a more appropriate system tool > > El mié, 24 mar 2021 a las 10:46, Sara da Cunha Monteiro de Souza (< > saramonteirosouz...@gmail.com>) escribió: > > > Hi Grr, > > > > I have never needed to use this function neither this range (ns). > > But I used the usleep function which resolution is defined as > > CONFIG_USEC_PER_TICK. > > But maybe, in your case, for such range, you should consider using a > > hardware timer or a Timer Hook. > > Take a look at this wiki: > > https://cwiki.apache.org/confluence/display/NUTTX/Short+Time+Delays > > > > Sara > > > > Em qua., 24 de mar. de 2021 às 13:37, Grr <gebbe...@gmail.com> escreveu: > > > > > Hello to all. > > > > > > Looking for the right way to create a _very_ short delay (10-100 ns), > > > I > > > found clock_nanosleep, whose description says: > > > > > > "The suspension time caused by this function may be longer than > > > requested > > > because the argument value is rounded up to an integer multiple of the > > > sleep resolution" > > > > > > What is the sleep resolution and where/how is defined? > > > > > > TIA > > > Grr > > > > > >
